The present invention relates to density-matched suspensions and, more particularly, in certain embodiments, to density-matched suspensions that comprise a solid particle suspended in a suspending liquid and associated methods of use.
Suspensions may be used in any number of applications where it may be desirable to suspend a solid particle in a suspending liquid for extended periods of time. For example, such applications may include cosmetics, pharmaceuticals, foodstuffs, agricultural products (e.g., fertilizers, pesticides, etc.), decorative mixtures, and downhole applications. In downhole applications, for example, downhole additives (such as water-soluble polymers) may be suspended in inert organic liquids to facilitate their handling and mixing with well treatment fluids, such as cement compositions.
In general, a suspension is typically formulated so that the solid particle should not undesirably settle out of the suspending liquid. To prevent sedimentation of the solid particle, the suspension typically may rely on viscosity. As used herein, a suspension that relies at least substantially on viscosity to prevent sedimentation of the solid particle is referred to as a “viscosity-controlled suspension.” By way of example, the liquid generally may have a viscosity sufficient to slow the sedimentation rate of the solid particle, which typically has a density greater than the suspending liquid. To provide the necessary viscosity, a suspending agent (e.g., hydrophobic polymers, organophilic clays, etc.) may be included in the viscosity-controlled suspension. However, reliance on viscosity to prevent sedimentation may be problematic. For instance, the viscosity of the suspending liquid may change with time such that the suspending liquid may not have a sufficient viscosity to prevent the undesired sedimentation of the solid particle. Accordingly, the viscosity-controlled suspensions may not have the desired shelf life.
As previously mentioned, downhole additives may be suspended in inert organic liquids to facilitate their handling and mixing with well treatment fluids. For example, fluid-loss-control additives (such as water-soluble polymers) may be suspended in an organic liquid to facilitate their handing and mixing with a cement composition. Such suspensions generally contain a high concentration of the fluid-loss-control additive, the organic liquid (e.g., mineral oil), a surfactant for enhancing the release of the polymer into an aqueous liquid, and a viscosifying agent (e.g., an organophilic clay). These suspensions, however, may be environmentally undesirable, particularly in highly regulated regions, because the organic liquid and/or the viscosifying agents may fail to satisfy the aquatic toxicity and/or biodegradability requirements that may be imposed in these regions. Moreover, in cement compositions that have been foamed, the organic liquid may lead to the undesired breaking of the foam, with a concomitant release of the foaming gas, causing high formation pressures and possible fracturing of the formation. Further, in cement compositions, the organic liquid may not be beneficial to the properties of the cement, in that the organic liquids do not bind to the cement, taking up volume that could be used to enhance the cement matrix.